The main objective of this proposal is a molecular description of the transport of vitamin B12 in cells of Escherichia coli. The specific aims for the coming 12-month period are purification and some structural studies on the B12 receptor sites located in the outer membrane of the cell envelope, and elucidation of the mechanism by means of which these sites communicate with the interior of the cell. The purification procedures will be based on affinity chromatography with adsorbents containing covalently linked corrinoid compounds. The B12 receptor sites are shared by colicins E1, E2 and E3 and with bacteriophage BF23. The structural requirements for receptor activity for each one of these substrates will be examined and compared. The mechanism of transfer of vitamin B12 from the outer membrane receptors into the interior of the cell will be probed by means of a variety of photo-affinity label derivatives of vitamin B12. BIBLIOGRAPHIC REFERENCES: Bradbeer, Clive, Marjess L. Woodrow, and Lilla I. Khalifah. Transport of vitamin B12 in Escherichia coli: Common receptor system for vitamin B12 and bacteriophage BF23 on the outer membrane of the cell envelope. J. Bacteriol. 125, 1032-1039 (1976). Kenley, Jane S., John C. White, Donna R. Di Masi, and Clive Bradbeer. Transport of vitamin B12 in Escherichia coli: Specificity of the B12 receptor. Fed. Proc. 35., 1700 (1976).